This invention relates to the structure and the manufacture of a roller sleeve and of a machine roll employing the sleeve. The invention attains rollers that have relatively low weight combined with other advantages, including high vibration damping, stable and precise dimensions, and a durable hard roller surface.
Machine rolls are used in various machines that manufacture, process or otherwise handle webs of material such as paper and fabric. A machine roll generally has three components, namely a cylindrical roller sleeve and two journals that mount the sleeve for rotation. The journals typically include hardened steel sleeves to reduce wear.
One exacting application of machine rolls is in the transfer of ink in a printing press. By way of example, a flexographic press that prints six or eight colors has printing plates located around a single central drum. Three rolls, termed an anilox roll, a plate cylinder roll, and a central drum roll, function together to print a color image. The anilox roll transfers ink to a printing plate that is attached to the plate cylinder roll. A conventional anilox roll has a hard ceramic surface coating that is laser-etched with up to 160,000 small pits per square inch, to control with precision the amount ink transferred to the printing plate. The plate cylinder roll is wrapped with the flexible printing plate. The printing plate picks up ink from the anilox roll and transfer it to the web that is being printed, e.g. a paper, film or foil. The central drum roll supports that web during ink transfer operations.
Conventional anilox rolls and plate cylinder rolls are typically of steel and weigh as much as 250 pounds each. The heavy rolls require mechanized lifting devices, can be time-consuming to change and are a safety hazard to handle.
Further, the anilox roll and the plate cylinder roll are subject to vibration. The vibration, which is due at least in part to the lower critical speeds of steel rolls, causes vibration at lower rpm. This vibration, and other resonances and bounce of the rolls, detract from the printing quality and from the line speed.
A further factor regarding anilox and plate cylinder rolls, and other kinds of machine rolls, is the requirement for exacting dimensional tolerances. For example, the outer diameter of the journals of a print roll, also termed a print cylinder, is to be precisely dimensioned with respect to the outer diameter of the cylinder roller surface; tolerances on concentricity, roundness and total indicator runout print (TIR) typically are on the order of .+-.0.0003 inch.
Accordingly, an object of this invention is to provide a machine roll that matches or exceeds the performance of prior metal rolls and has significantly less weight.
Another object of this invention is to provide a machine roll that has relatively low weight and that damps vibration, such as mechanically induced vibration as caused by rotation of the roller and by the printing process.
A further object of this invention is to provide a roller sleeve for assembly into a machine roll having the foregoing features.
It also an object of this invention to provide a method for manufacture of such roller sleeves and machine rolls.
Other objects of the invention will in part be obvious and in part appear hereinafter.